This invention relates to rotary piston mechanisms and more particularly, to such a mechanism for internal combustion engines, fluid motors, pumps and the like, wherein a rotating piston or rotor captured in a chamber moves eccentrically with respect to an output or an input drive shaft eminating therefrom.
Heretofore, rotary piston mechanisms for use as fluid pumps have been proposed comprising a three tooth external gear and a two tooth internal gear rotating therein. The external gear is a chamber having three equal curvilinear walls which are concave with respect to the chamber axis and an elongated rotor that rotates on a rotor axle that moves in a circular orbit about the chamber axis. The rotor is of constant width and is rounded at the ends which fit into the corner spaces of the internal gear between the concave walls, and so fluid drawn into the chamber is forced by the rotor to these corners. In operation, the rotor contacts, rolls and slides along the three walls of the chamber in succession. This type of rotary piston mechanism has not been proposed for use in an internal combustion engine, because the rotor would have to seal against the chamber to hold high pressure gas and it would be very difficult to seal the rolling, sliding action of the rotor against the chamber walls.
Rotary piston internal combustion engines exemplified by the Wankel type engine have a generally triangular shaped rotor in an oblong chamber. The rotor is eccentrically driven in the chamber as it rides eccentrically about a fixed centrally located gear. Thus, the output drive shaft connected to the rotor is driven at the same rotation rate as the rotor. The three points of the rotor are equipped with sliding seals that engage the inner walls of the chamber and divide the chamber into three spaces, each bounded by each one of the faces of the rotor. During each complete revolution of the rotor, each of these spaces moves around the chamber increasing and decreasing in size to perform the four functions of intake, compression, power and exhaust as a gasoline, air mixture is drawn into the space, compressed, combusted to deliver power as it expands, and then, finally, exhausted. These functions are performed in all three of the spaces during each rotation of the rotor in the chamber and the power function is performed consecutively in the spaces always along the same portion of the walls of the chamber. The other functions are also performed consecutively in each of the spaces and each of them is also performed along a given portion of the walls of the chamber. Thus, the combustion and exhaust functions which inflict the greatest wear on the walls of the chamber, occur repeatedly along the same portions of the chamber walls and so, the effectiveness of the seals carried at each of the points of the rotor are inclined to degrade along these portions of the chamber walls.
It is intrinsic to the Wankel type engine and to any type rotary piston mechanism that uses a triangular shaped rotor which seals against the chamber walls at the points of the triangle, that the chamber be epitrochoidal with two symmetrical cusps. Hence, with respect to the axis of the chamber, the walls of the chamber are curvilinear and concave at all points except at the two cusps. At that point, the walls are generally convex with respect to the chamber axis, and so the seals must follow a concave wall which changes abruptly to convex at two points along a complete cycle of travel of the seal against the wall. Hence, the angle the seal subtends with the wall is not constant during the entire travel of the seal along the wall. In fact, that angle becomes exceedingly acute as it moves along the wall from a convex portion of the wall to a concave portion. The effectiveness of the seal where the angle is exceedingly acute, is diminished and the seals have a tendency to leak at such points.